1. Field of the Invention
This invention relates to an anamorphic optical system having a plastic lens, and in particular relates to an anamorphic optical system of which the focal point suffers little displacement due to temperature changes.
2. Description of the Prior Art
Conventionally, the f.theta. lens used in laser printers is generally an anamorphic lens system comprising two glass lenses. Glass anamorphic lenses are however costly as they must be ground to specifications.
Plastic lenses have thus been proposed to lower manufacturing costs as they do not require grinding.
Plastic lenses show a greater variation of refractive index and linear expansion due to temperature changes, however, and their imaging performance is easily impaired due to displacement of the focal point. In devices such as laser printers where no provision is made for focusing, therefore, it has been difficult to employ plastic lenses.